[elhigh]

Wow, Wisconsin. Milwaukee, no less. I envy your real winters (don't get much of that in E. TN) and cheese curds. I lurves me some cheese curds.

Is your crawlspace insulated? I'm assuming it must be, since it's part of the air return plenum. That's good. We're learning that crawlspaces pretty much everywhere should be considered part of the house envelope and should be sealed, insulated, and conditioned along with the rest of the house. Knowing that, I can make this recommendation: the radiator idea is workable. You don't have to have antifreeze running through the loop, since the crawlspace is conditioned space: it should never go below freezing.

The bad news: an actual radiator isn't your best choice for getting heat out of the woodstove and into your coil. What you want is a big, flat, full-contact plate with coils running through it either attached directly to the woodstove, or coils inside the woodstove itself. I'm not positive how you would go about doing this, but one way to start is to construct your coil according to the size of the woodstove surface you intend to use, form up around the perimeter of that surface, and then pour a monolithic slab of stucco mix directly on the woodstove. You will need to do this when the weather is warm so you can orient the woodstove, and you will need to provide a means of attaching the slab to the woodstove, since masonry products don't generally adhere to metals well. Once that's done, it's a simple matter of running the coil to wherever you want the radiant heat.

Warning: concrete and stucco stick to aluminum pretty well, but I don't recommend you rely on it for attachment if that's what your stove is made of (and I don't know of any that are) - the differences of thermal expansion would probably crack your collector plate pretty badly, or cause stove warpage.

Get a plain ol' box fan and set that near the stove, set on Low. It won't make a lot of noise, but it will get a lot of heat off the stove and around the house. Another fan that blows cool air along the floor from a cold part of the house toward the stove will tend to push warm air along the ceiling toward where that fan is: also very good. I haven't had much luck getting that to work in my house from the second level, though, and mine is also a 1.5 story.

Good luck - there's lots of interesting things to do with your situation, some of which you can do immediately for really low outlay and surprising results.